Delayed neutrons yields and group abundances for thermal-neutron-induced fission of 233U

• A new dataset of delayed neutron parameters associated to the thermal fission of 233 U. • Total delayed neutron yield is measured with an uncertainty below 1 % • Delayed neutron groups’ abundances were fitted to data and found in good agreement with previous estimation. In the field of nuclear reactor physics, the precise measurement of delayed neutrons (DN) is crucial for accurately predicting reactor behavior and ensuring safety. This article focuses on the measurement of DN parameters for 233 U, conducted at the Institut Laue-Langevin (ILL, Grenoble, France). Aimed at enhancing the accuracy of nuclear reactor models, the study was part of the ALDEN project, spearheaded by CEA, to improve data on DN emission from fission reactions, with a specific focus on key actinides like 235 U, 239 Pu, 233 U and 241 Pu. Already used in a previous experiment on 235 U, the experimental setup comprised a CEA-made active fissile target, a dual-beam shutter to interrupt neutrons hitting the target, a detection system based on 3 He proportional counters, and an ILL-developed acquisition system. In this study, several irradiation campaigns were exploited to produce the total DN yield and the DN abundances by group associated to the thermal fission of 233 U. Our analysis made use of ratios between prompt and delayed neutrons, which led to very low uncertainties (below 1 %) compared to other methods. The CEA-developed CONRAD software was used to fit the decay of DN precursors. A total DN yield of 6.74 10 -3 ± 5 10 -5 was estimated, which is in good agreement with previous values reported in the literature. A set of groups’ abundances was also determined with a consistence covariance matrix. Using this set of abundances, a DN mean-life of 12.62 ± 0.08 s was estimated. In the future, other fissile actinides will be subject to similar studies in the frame of the ALDEN project.